Tire

ABSTRACT

A tire has a tread portion including a first land portion including first and second circumferential edges and and a tread surface. On the first land portion, curved grooves are provided in a tire circumferential direction. Each curved groove extends from a first end on the first circumferential edge side, terminates at a second end within the first land portion, and includes first and second curved portions and on the first end and second end sides, respectively. The first curved portion is an arc curve with a radius of curvature having a center on the first circumferential edge side of the curved groove. The second curved portion is an arc curve with a radius of curvature having a center on the second circumferential edge side of the curved groove.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a tire.

Description of the Background Art

Japanese Laid-Open Patent Publication No. 2018-114846 discloses a tirehaving improved running performance on a dry road surface and an ice andsnow road surface by improving the arrangement of grooves.

In recent years, with enhancement of the performance of vehicles, tiresthat exhibit more excellent on-snow performance have been required.Meanwhile, depending on the shapes of grooves, steering stability on adry road surface may be deteriorated with improvement of on-snowperformance.

The present invention has been made in view of the above-describedproblem, and a main object of the present invention is to provide a tirethat can exhibit excellent on-snow performance while maintainingsteering stability on a dry road surface.

SUMMARY OF THE INVENTION

The present invention is directed to a tire having a tread portion,wherein: the tread portion includes a first land portion; the first landportion includes a first circumferential edge, a second circumferentialedge, and a tread surface between the first circumferential edge and thesecond circumferential edge; on the first land portion, a plurality ofcurved grooves are provided in a tire circumferential direction; each ofthe curved grooves extends from a first end on the first circumferentialedge side and terminates at a second end within the first land portion;each of the curved grooves includes a first curved portion on the firstend side, and a second curved portion on the second end side; the firstcurved portion is an arc curve with a radius of curvature having acenter on the first circumferential edge side of the curved groove; andthe second curved portion is an arc curve with a radius of curvaturehaving a center on the second circumferential edge side of the curvedgroove.

In the tire according to the present invention, the first curved portionpreferably crosses a center position in a tire axial direction of thefirst land portion.

In the tire according to the present invention, the second curvedportion preferably crosses the center position in the tire axialdirection of the first land portion.

In the tire according to the present invention, the second end ispreferably located between the first circumferential edge and the centerposition in the tire axial direction of the first land portion.

In the tire according to the present invention, a groove width of eachof the curved grooves preferably gradually decreases from the first endtoward the second end.

In the tire according to the present invention, the groove width of eachof the curved grooves is preferably 2 to 4 mm.

In the tire according to the present invention, the radius of curvatureof the second curved portion is preferably larger than the radius ofcurvature of the first curved portion.

In the tire according to the present invention, the radius of curvatureof the first curved portion is preferably 10 to 30 mm.

In the tire according to the present invention, the radius of curvatureof the second curved portion is preferably 30 to 60 mm.

In the tire according to the present invention, a length in the tirecircumferential direction of the first curved portion is preferably 30%to 70% of a length in the tire circumferential direction of the curvedgroove.

In the tire according to the present invention, the tread portionpreferably includes four land portions demarcated by main groovescontinuous in the tire circumferential direction.

In the tire according to the present invention, preferably, the tire hasa designated mounting direction to a vehicle, the tread portion includesa first tread edge located on an outer side of the vehicle when the tireis mounted on the vehicle, a second tread edge located on an inner sideof the vehicle when the tire is mounted on the vehicle, a first shouldermain groove continuously extending in the tire circumferential directionbetween the first tread edge and a tire equator, and a crown main grooveadjacent to the second tread edge side of the first shoulder maingroove, and the first land portion is demarcated between the firstshoulder main groove and the crown main groove.

On the first land portion of the tire according to the presentinvention, a plurality of curved grooves are provided in the tirecircumferential direction. Each curved groove extends from a first endon the first circumferential edge side of the first land portion andterminates at a second end within the first land portion. Such a curvedgroove serves to inhibit an excessive reduction in the stiffness of thefirst land portion and maintain steering stability on a dry roadsurface.

Each curved groove includes a first curved portion on the first endside, and a second curved portion on the second end side. The firstcurved portion is an arc curve with a radius of curvature having acenter on the first circumferential edge side of the curved groove, andthe second curved portion is an arc curve with a radius of curvaturehaving a center on the second circumferential edge side of the curvedgroove. The edges of the first curved portion and the second curvedportion of such a curved groove can provide frictional force in multipledirections during cornering on a strongly compacted snow road andenhance on-snow performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a development of a tread portion of a tire according to anembodiment of the present invention;

FIG. 2 is an enlarged view of a first land portion in FIG. 1 ;

FIG. 3 is a cross-sectional view taken along a line A-A in FIG. 2 ;

FIG. 4 is a cross-sectional view taken along a line B-B in FIG. 2 ;

FIG. 5 is an enlarged view of the contour of a curved groove;

FIG. 6 is a cross-sectional view taken along a line C-C in FIG. 5 ;

FIG. 7 is a cross-sectional view taken along a line D-D in FIG. 5 ;

FIG. 8 is a transverse cross-sectional view of a fourth tie bar in FIG.7 ;

FIG. 9 is a cross-sectional view taken along a line E-E in FIG. 5 ;

FIG. 10 is an enlarged view of a triangular block in FIG. 2 ;

FIG. 11 is an enlarged view of a second land portion and a fourth landportion;

FIG. 12 is an enlarged view of a third land portion; and

FIG. 13 is an enlarged view of a first land portion of a tire of acomparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. FIG. 1 is a development of a treadportion 2 of a tire 1 showing the embodiment of the present invention.The tire 1 according to the present embodiment is suitably used, forexample, as a pneumatic tire for a passenger car. However, the presentinvention is not limited to such a mode, and may be applied to aheavy-duty pneumatic tire and a non-pneumatic tire the interior of whichis not filled with pressurized air.

As shown in FIG. 1 , the tire 1 according to the present embodiment hasthe tread portion 2 having a designated mounting direction to a vehicle.The tread portion 2 has a first tread edge Te1 located at the outer sideof a vehicle when the tire 1 is mounted on the vehicle, and a secondtread edge Te2 located at the inner side of the vehicle when the tire 1is mounted on the vehicle. The mounting direction to a vehicle isindicated, for example, on a sidewall portion (not shown) by charactersor symbols.

In the case of a pneumatic tire, each of the first tread edge Te1 andthe second tread edge Te2 is a ground contact position at the outermostside in the tire axial direction when a normal load is applied to thetire 1 in a normal state and the tire 1 is brought into contact with aflat surface at a camber angle of 0°. The normal state is a state wherethe tire is mounted to a normal rim and inflated to a normal internalpressure and no load is applied to the tire. In the present description,unless otherwise specified, dimensions and the like of components of thetire are values measured in the normal state.

The “normal rim” is a rim that is defined, in a standard systemincluding a standard on which the tire is based, by the standard foreach tire, and is, for example, the “standard rim” in the JATMAstandard, the “Design Rim” in the TRA standard, or the “Measuring Rim”in the ETRTO standard.

The “normal internal pressure” is an air pressure that is defined, in astandard system including a standard on which the tire is based, by thestandard for each tire, and is the “maximum air pressure” in the JATMAstandard, the maximum value indicated in the table “TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES” in the TRA standard, or the “INFLATIONPRESSURE” in the ETRTO standard.

The “normal load” is a load that is defined, in a standard systemincluding a standard on which the tire is based, by the standard foreach tire, and is the “maximum load capacity” in the JATMA standard, themaximum value indicated in the table “TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES” in the TRA standard, or the “LOAD CAPACITY” in theETRTO standard.

The tread portion 2 includes a plurality of main grooves 3 continuouslyextending in the tire circumferential direction between the first treadedge Te1 and the second tread edge Te2, and a plurality of land portions4 demarcated by these main grooves 3. The tread portion 2 of the presentembodiment includes three main grooves 3 and four land portions 4.However, the tire according to the present invention is not limited tosuch a mode.

The main grooves 3 include a first shoulder main groove 5 providedbetween the first tread edge Te1 and a tire equator C, a second shouldermain groove 6 provided between the second tread edge Te2 and the tireequator C, and a crown main groove 7 provided between the first shouldermain groove 5 and the second shoulder main groove 6.

The distance La in the tire axial direction from the tire equator C tothe groove center line of the first shoulder main groove 5 or the secondshoulder main groove 6 is, for example, preferably 0.20 to 0.35 times atread width TW. The distance Lb in the tire axial direction from thetire equator C to the groove center line of the crown main groove 7 is,for example, preferably not greater than 0.15 times the tread width TW.The tread width TW is the distance in the tire axial direction from thefirst tread edge Te1 to the second tread edge Te2 in the normal state.

The crown main groove 7 of the present embodiment is provided, forexample, on the second tread edge Te2 side with respect to the tireequator C. However, the position of the crown main groove 7 is notlimited to such a position.

Each main groove 3 of the present embodiment extends, for example, in astraight manner so as to be parallel to the tire circumferentialdirection. Each main groove 3 may extend, for example, in a wavy manner.

The groove width Wa of each main groove 3 is, for example, preferably5.0% to 8.0% of the tread width TW. In the present specification, thegroove width is the distance between the groove edges in a directionorthogonal to the groove center line. In a preferable mode, the groovewidth of the second shoulder main groove 6 is larger than the groovewidth of the first shoulder main groove 5, and the groove width of thecrown main groove 7 is larger than the groove width of the secondshoulder main groove 6. In the case of a pneumatic tire for a passengercar, the depth of each main groove 3 is, for example, preferably 5 to 10mm.

The land portions 4 include a first land portion 11, a second landportion 12, a third land portion 13, and a fourth land portion 14. Thefirst land portion 11 is demarcated between the first shoulder maingroove 5 and the crown main groove 7. The second land portion 12 isdemarcated between the second shoulder main groove 6 and the crown maingroove 7. The third land portion 13 is demarcated between the firstshoulder main groove 5 and the first tread edge Te1. The fourth landportion 14 is demarcated between the second shoulder main groove 6 andthe second tread edge Te2.

FIG. 2 shows an enlarged view of the first land portion 11. As shown inFIG. 2 , the first land portion 11 of the present embodiment has alargest width W1 in the tire axial direction among the four landportions 4. In the tread portion 2 which includes the four land portions4, a great contact pressure acts on the first land portion 11 duringstraight running and during cornering, but, in the present embodiment,the first land portion 11 has the largest width in the tire axialdirection among the four land portions 4 and has high stiffness.Therefore, steering stability on a dry road surface is improved. Thewidth W1 of the first land portion 11 is, for example, preferably 0.25to 0.40 times of the tread width TW (shown in FIG. 1 , and the sameapplies below).

The first land portion 11 includes a first circumferential edge 11 a, asecond circumferential edge 11 b, and a tread surface 11 c between thefirst circumferential edge 11 a and the second circumferential edge 11b. The first circumferential edge 11 a is the circumferential edge onthe first shoulder main groove 5 side of the first land portion 11, andthe second circumferential edge 11 b is the circumferential edge on thecrown main groove 7 side of the first land portion 11.

On the first land portion 11, a plurality of curved grooves 15 areprovided in the tire circumferential direction. Each curved groove 15extends from a first end 15 a on the first circumferential edge 11 aside and terminates at a second end 15 b within the first land portion11. Such a curved groove 15 serves to inhibit an excessive reduction inthe stiffness of the first land portion 11 and maintain steeringstability on a dry road surface.

The curved groove 15 includes a first curved portion 16 on the first end15 a side, and a second curved portion 17 on the second end 15 b side.The first curved portion 16 is an arc curve with a radius of curvaturehaving a center on the first curved edge 11 a side of the curved groove15. The second curved portion 17 is an arc curve with a radius ofcurvature having a center on the second circumferential edge 11 b sideof the curved groove 15. The edges of the first curved portion 16 andthe second curved portion 17 of such a curved groove 15 can providefrictional force in multiple directions during cornering on a stronglycompacted snow road and enhance on-snow performance.

Hereinafter, the specific configuration of the tire according to thepresent embodiment will be described. The first land portion 11 of thepresent embodiment has, for example, a plurality of first inclinedgrooves 21 and a plurality of second inclined grooves 22.

Each first inclined groove 21 extends, for example, so as to be inclinedin a first direction (upward toward the right side in FIG. 2 ) relativeto the tire axial direction. Each first inclined groove 21 of thepresent embodiment extends from the first circumferential edge 11 a tothe second circumferential edge 11 b and traverses the first landportion 11. The first inclined groove 21 is inclined, for example, at anangle θ1 of 10 to 60° relative to the tire axial direction. The angle ofthe first inclined groove 21 relative to the tire axial directionpreferably gradually increases toward the second circumferential edge 11b side, for example. Each first inclined groove 21 of the presentembodiment is curved in an arc shape with a radius of curvature of 50 to150 mm, for example. Such a first inclined groove 21 can providefrictional force in multiple directions during running on snow.

FIG. 3 shows a cross-sectional view of the first inclined groove 21taken along a line A-A in FIG. 2 . As shown in FIG. 3 , the firstinclined groove 21 includes a first tie bar 23 raised at a groove bottomon the first circumferential edge 11 a (shown in FIG. 2 , and the sameapplies below) side. The first tie bar 23 of the present embodiment isprovided, for example, in an end portion on the first circumferentialedge 11 a side of the first inclined groove 21. The first tie bar 23has, for example, a constant depth in the longitudinal direction of thefirst inclined groove 21. The depth d2 of the first tie bar 23 is 45% to60% of the maximum depth d1 of the first inclined groove 21. The firstinclined groove 21 including such a first tie bar 23 can enhance on-snowperformance while inhibiting a reduction in the stiffness of the firstland portion 11.

As shown in FIG. 2 , each second inclined groove 22 is, for example,inclined from the second circumferential edge 11 b in a second direction(downward toward the right side in FIG. 2 ) opposite to the firstdirection and terminates within the first land portion 11. The secondinclined groove 22 is inclined, for example, at an angle θ2 of 10 to 60°relative to the tire axial direction. The angle of the second inclinedgroove 22 relative to the tire axial direction preferably graduallyincreases toward the first circumferential edge 11 a side, for example.Each second inclined groove 22 of the present embodiment is curved in anarc shape with a radius of curvature of 50 to 150 mm, for example.

The second inclined groove 22 communicates with the first inclinedgroove 21, for example, and preferably intersects the first inclinedgroove 21. Each second inclined groove 22 of the present embodimentintersects the first inclined groove 21 on the first circumferentialedge 11 a side with respect to a center position 20 in the tire axialdirection of the first land portion 11. In a more preferable mode, thesecond inclined groove 22 intersects the first inclined groove 21 on thesecond circumferential edge 11 b side with respect to the first tie bar23 (shown in FIG. 3 ) of the first inclined groove 21. Such a secondinclined groove 22 can form a hard snow column at the intersection withthe first inclined groove 21 and provide large snow column shearingforce during running on snow.

FIG. 4 shows a cross-sectional view of the second inclined groove 22taken along a line B-B in FIG. 2 . As shown in FIG. 4 , the secondinclined groove 22 includes a second tie bar 24 raised at a groovebottom in an end portion at the first circumferential edge 11 a. Thesecond tie bar 24 of the present embodiment has, for example, aninclined bottom surface, and the depth thereof gradually decreasestoward the first circumferential edge 11 a side. The maximum depth d4 ofthe second tie bar 24 is 60% to 75% of the maximum depth d3 of thesecond inclined groove 22, and is preferably larger than the depth d2(shown in FIG. 3 ) of the first tie bar 23. The minimum depth d5 of thesecond tie bar 24 is 35% to 45% of the maximum depth d3 of the secondinclined groove 22, and is preferably smaller than the depth d2 of thefirst tie bar 23. The second inclined groove 22 including such a secondtie bar 24 serves to enhance steering stability on a dry road surfaceand on-snow performance in a well-balanced manner.

As shown in FIG. 2 , each curved groove 15 intersects a curved groove 15adjacent thereto in the tire circumferential direction. Each curvedgroove 15 of the present embodiment extends from the first end 15 a andintersects the second inclined groove 22. In addition, the curved groove15 extends from the second inclined groove 22 toward the second end 15 bside and intersects the first inclined groove 21 that intersects thesecond inclined groove 22. Moreover, the curved groove 15 extends fromthe first inclined groove 21 toward the second end 15 b side andintersects the curved groove 15 adjacent thereto in the tirecircumferential direction. Furthermore, the second end 15 b of thecurved groove 15 is located between the first circumferential edge 11 aand the center position 20 in the tire axial direction of the first landportion 11. In a preferable mode, the second end 15 b of the curvedgroove 15 is located on the second circumferential edge 11 b side withrespect to the terminal end of the second inclined groove 22.

The groove width of the curved groove 15 preferably gradually decreasesfrom the first end 15 a toward the second end 15 b. The groove width ofthe curved groove 15 is, for example, 2 to 5 mm.

FIG. 5 shows an enlarged view of the contour of the curved groove 15. InFIG. 5 , for ease of understanding the configuration of the curvedgroove 15, other grooves are omitted except portions that intersect thecurved groove 15. As shown in FIG. 5 , the first curved portion 16 ofthe curved groove 15 crosses the center position 20 in the tire axialdirection of the first land portion 11, for example. The first curvedportion 16 is, for example, formed between the first end 15 a and thefirst inclined groove 21 and intersects the second inclined groove 22.The radius of curvature of the first curved portion 16 is, for example,10 to 30 mm.

The first curved portion 16 includes a first portion 26 extending fromthe first end 15 a to the second inclined groove 22, and a secondportion 27 extending from the second inclined groove 22 to the firstinclined groove 21. Each of the first portion 26 and the second portion27 is curved. The first portion 26 extends, for example, so as to beinclined in the first direction, and extends along the first inclinedgroove 21 in the present embodiment. The second portion 27 is curved,for example, so as to be convex on the second circumferential edge 11 bside.

The groove width of the second portion 27 is, for example, 2 to 5 mm.The second portion 27 is curved, for example, with a radius of curvatureof 15 to 30 mm. The radius of curvature of the second portion 27 ispreferably smaller than the radius of curvature of the first portion 26.The curved groove 15 including such a second portion 27 serves tofurther enhance on-snow performance.

The length L2 in the tire circumferential direction of the first curvedportion 16 is preferably not less than 30% and more preferably not lessthan 40%, and is preferably not greater than 70% and more preferably notgreater than 60%, of the length L1 in the tire circumferential directionof the curved groove 15. Each length of the curved groove 15 is, forexample, measured along the groove center line.

FIG. 6 shows a cross-sectional view of the first portion 26 taken alonga line C-C in FIG. 5 . As shown in FIG. 6 , the first portion 26 is, forexample, preferably provided with a third tie bar 28 raised at a groovebottom on the first end 15 a side of the curved groove 15. Theconfiguration of the first tie bar 23 of the first inclined groove 21can be applied to the third tie bar 28 of the first portion 26. Such afirst portion 26 can enhance on-snow performance while maintainingsteering stability on a dry road surface.

FIG. 7 shows a cross-sectional view of the second portion 27 taken alonga line D-D in FIG. 5 . As shown in FIG. 7 , the second portion 27 isprovided with a fourth tie bar 29 raised at a groove bottom in a centerportion in the longitudinal direction thereof. The depth d7 of thefourth tie bar 29 is 50% to 70% of the maximum depth d6 of the secondportion 27.

FIG. 8 shows a cross-sectional view, of the fourth tie bar 29,orthogonal to the longitudinal direction of the second portion 27. Asshown in FIG. 8 , the fourth tie bar 29 preferably has a groove bottomsipe 31 that is open at the groove bottom and that extends in thelongitudinal direction of the second portion 27. Such a groove bottomsipe 31 can inhibit clogging of the second portion 27 with snow. In thepresent specification, the term “sipe” means a slit having a width notgreater than 1.5 mm.

As shown in FIG. 5 , the second curved portion 17 of the curved groove15 extends, for example, so as to be inclined in the second direction,and extends along the second inclined groove 22 in the presentembodiment. The second curved portion 17 crosses the center position 20in the tire axial direction of the first land portion 11, for example.The second curved portion 17 is, for example, formed between the firstinclined groove 21 and the second end 15 b and intersects the curvedgroove 15 adjacent thereto in the tire circumferential direction.

The radius of curvature of the second curved portion 17 is preferablylarger than the radius of curvature of the first curved portion 16. Theradius of curvature of the second curved portion 17 is, for example, 30to 60 mm. Accordingly, the curved groove 15 is less likely to be cloggedwith snow during running on snow, and excellent on-snow performance iscontinuously exhibited.

The length L3 in the tire circumferential direction of the second curvedportion 17 is smaller than the length L2 in the tire circumferentialdirection of the first curved portion 16. The length L3 of the secondcurved portion 17 is preferably not less than 20% and more preferablynot less than 30%, and is preferably not greater than 50% and morepreferably not greater than 40%, of the length L1 in the tirecircumferential direction of the curved groove 15.

FIG. 9 shows a cross-sectional view of the second curved portion 17taken along a line E-E in FIG. 5 . As shown in FIG. 9 , the secondcurved portion 17 is, for example, provided with a fifth tie bar 30raised at a groove bottom in an end portion on the first inclined groove21 side. The depth d9 of the fifth tie bar 30 is, for example, 50% to70% of the maximum depth d8 of the second curved portion 17. The secondcurved portion 17 having such a fifth tie bar 30 serves to enhancesteering stability on a dry road surface and on-snow performance in awell-balanced manner.

An end portion 32 on the second end 15 b side of the second curvedportion 17 of the present embodiment has a depth that graduallydecreases toward the second end 15 b side. Accordingly, the end portion32 has a bottom surface curved in an arc shape. Therefore, uneven wearis inhibited around the end portion 32.

As shown in FIG. 2 , the first land portion 11 is divided into aplurality of blocks by providing the above-described first inclinedgrooves 21, second inclined grooves 22, and curved grooves 15 thereon.The first land portion 11 of the present embodiment includes a pluralityof block elements 33 each demarcated between two first inclined grooves21.

Each block element 33 includes, for example, a quadrangular block 34having a substantially quadrangular tread surface, and a triangularblock 35 having a substantially triangular tread surface. Thequadrangular block 34 includes a part of the first circumferential edge11 a and is demarcated by two first inclined grooves 21 and a secondinclined groove 22. The triangular block 35 is demarcated by a firstinclined groove 21, a second inclined groove 22, and the secondcircumferential edge 11 b. The triangular block 35 is, for example,located on the tire equator C. In the present embodiment, the triangularblock 35 is also located on the center position 20 in the tire axialdirection of the first land portion 11. In the triangular block 35, 50%or more of the area of the tread surface thereof is preferably locatedon the second tread edge Te2 side with respect to the center position20.

The quadrangular block 34 has, for example, a plurality of sipes 40inclined in the first direction. Each sipe 40 extends, for example,along the first inclined groove 21. The sipes 40 provided on thequadrangular block 34 include, for example, a first sipe 41, a secondsipe 42, and a third sipe 43. The first sipe 41 extends from the firstcircumferential edge 11 a to the second inclined groove 22. The secondsipe 42 extends from the first circumferential edge 11 a to the secondcurved portion 17 of the curved groove 15. The third sipe 43 extendsfrom the second curved portion 17 to the second inclined groove 22. Eachof such sipes 40 can provide frictional force during running on snowwhile inhibiting uneven wear of the first land portion 11.

FIG. 10 shows an enlarged view of the triangular block 35. The length L4in the tire axial direction of the triangular block 35 is, for example,0.50 to 0.80 times the width W1 (shown in FIG. 2 ) in the tire axialdirection of the first land portion 11.

The second portion 27 of the first curved portion 16 of the curvedgroove 15 traverses the triangular block 35, for example. In apreferable mode, the curved groove 15 communicates with the firstinclined groove 21 and the second inclined groove 22 on the secondcircumferential edge 11 b side with respect to the center position 20(shown in FIG. 2 ) in the tire axial direction of the first land portion11 and traverses the triangular block 35. Accordingly, the triangularblock 35 includes an end portion 36 demarcated by the first inclinedgroove 21, the second inclined groove 22, and the second portion 27. Thelength L5 in the tire axial direction of the end portion 36 is, forexample, preferably not less than 30% and more preferably not less than40%, and is preferably not greater than 70% and more preferably notgreater than 60%, of the length L4 in the tire axial direction of thetriangular block 35. Such a triangular block 35 can ensure stiffness inthe tire axial direction and maintain steering stability on a dry roadsurface.

At the end portion 36, an angle θ3 between an edge 36 a on the firstinclined groove 21 side and an edge 36 b on the second inclined groove22 side is, for example, 40 to 80°. Such an end portion 36 can enhancewet performance while inhibiting chipping of the triangular block 35during running. The angle θ3 corresponds to the angle between thetangent to the edge 36 a at a top 36 c of the end portion 36 and thetangent to the edge 36 b at the top 36 c.

The triangular block 35 preferably has a fourth sipe 44 and a fifth sipe45 inclined in the second direction. The fourth sipe 44 and the fifthsipe 45 extend from the second circumferential edge 11 b and terminatebefore reaching the second portion 27 of the first curved portion 16.The length in the tire axial direction of the fifth sipe 45 is largerthan the length in the tire axial direction of the fourth sipe 44.

FIG. 11 shows an enlarged view of the second land portion 12 and thefourth land portion 14. As shown in FIG. 11 , each of the width W2 inthe tire axial direction of the second land portion 12 and the width W4in the tire axial direction of the fourth land portion 14 is preferably0.10 to 0.20 times the tread width TW.

The second land portion 12 has a plurality of first lateral grooves 46and a plurality of termination grooves 47. Each first lateral groove 46fully traverses the second land portion 12, for example. Eachtermination groove 47 extends from the second shoulder main groove 6 andterminates within the second land portion 12, for example. Such a firstlateral groove 46 and such a termination groove 47 serve to enhancesteering stability on a dry road surface and on-snow performance in awell-balanced manner.

In a preferable mode, an end portion on the crown main groove 7 side ofthe first lateral groove 46 preferably overlaps a region obtained byextending an end portion on the second circumferential edge 11 b side ofthe first inclined groove 21 so as to be parallel to the tire axialdirection. In addition, the first lateral groove 46 preferably overlapsa region obtained by extending the second inclined groove 22 whilemaintaining the inclination direction and the curvature thereof.Accordingly, during running on snow, the first lateral groove 46 forms alarge snow column together with the first inclined groove 21 and thesecond inclined groove 22, so that on-snow performance is furtherenhanced.

The second land portion 12 of the present embodiment has connectionsipes 48 that extend from the termination grooves 47 to the crown maingroove 7, and termination sipes 49 that extend from the second shouldermain groove 6 and that terminate within the second land portion 12. Suchconnection sipes 48 and termination sipes 49 can provide frictionalforce during running on snow while inhibiting uneven wear of the secondland portion 12.

The fourth land portion 14 has a plurality of second lateral grooves 50and a plurality of first transverse sipes 51. Each of the second lateralgrooves 50 and the first transverse sipes 51 traverses the fourth landportion 14.

An end portion on the second shoulder main groove 6 side of each secondlateral groove 50 preferably overlaps a region obtained by extending anend portion on the second shoulder main groove 6 side of the firstlateral groove 46 or the termination groove 47, which is provided on thethird land portion 13, so as to be parallel to the tire axial direction.Accordingly, the second lateral groove 50 and the first lateral groove46 or the termination groove 47 become integrated to form a large snowcolumn during running on snow, so that excellent on-snow performance isexhibited.

FIG. 12 shows an enlarged view of the third land portion 13. As shown inFIG. 12 , the width W3 in the tire axial direction of the third landportion 13 is, for example, 0.10 to 0.25 times of the tread width TW. Ina preferable mode, the width W3 of the third land portion 13 is largerthan the width W2 (shown in FIG. 11 ) in the tire axial direction of thesecond land portion 12 and the width W4 (shown in FIG. 11 ) in the tireaxial direction of the fourth land portion 14.

The third land portion 13 has a plurality of third lateral grooves 53and a plurality of second transverse sipes 54. Each of the third lateralgrooves 53 and the second transverse sipes 54 traverses the third landportion 13.

An end portion on the first shoulder main groove 5 side of each thirdlateral groove 53 preferably overlaps a region obtained by extending anend portion on the first shoulder main groove 5 side of the firstinclined groove 21 or the curved groove 15, which is provided on thefirst land portion 11, so as to be parallel to the tire axial direction.Accordingly, the third lateral groove 53 and the first inclined groove21 or the curved groove 15 become integrated to form a large snow columnduring running on snow, so that excellent on-snow performance isexhibited.

Although the tire according to the embodiment of the present inventionhas been described in detail above, the present invention is not limitedto the above specific embodiment, and various modifications can be madeto implement the present invention.

EXAMPLES

Tires with a size of 215/60R16 having the basic pattern in FIG. 1 wereproduced as test tires. As a comparative example, a tire having firstland portions a shown in FIG. 13 was produced as a test tire. In thetire of the comparative example, a first curved portion c and a secondcurved portion d of each curved groove b are each formed by an arc curvewith a radius of curvature having a center on the first circumferentialedge side. The tire of the comparative example has substantially thesame pattern as shown in FIG. 1 , except for the above matters. Therespective test tires were tested for steering stability on a dry roadsurface and on-snow performance. The common specifications and the testmethods for the respective test tires are as follows.

Mount rim: 16×6.5

Tire internal pressure: 240 kPa

Test vehicle: a front-wheel-drive car having an engine displacement of2500 cc

Tire mounted position: all wheels

<Steering Stability on Dry Road Surface>

Sensory evaluation was made by a driver for steering stability when thedriver drove the above test vehicle on a dry road surface. The resultsare indicated as scores with the score of the comparative example beingregarded as 100. A higher value indicates that the steering stability ona dry road surface is better. As for the scores, 95 points or more isacceptable, and 98 points or more is more preferable.

<On-Snow Performance>

Sensory evaluation was made by a driver for performance when the driverdrove the above test vehicle on a snow road. The results are indicatedas scores with the score of the comparative example being regarded as100. A higher value indicates that the on-snow performance is better. Asfor the scores, 95 points or more is acceptable, and 98 points or moreis more preferable.

The test results are shown in Table 1.

TABLE 1 Comparative Example Example Example Example Example ExampleExample Example Example Example 1 2 3 4 5 6 7 8 9 Drawing showing firstFIG. 13 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2land portion Radius of curvature — 20 10 15 25 30 20 20 20 20 (mm) offirst curved portion Radius of curvature — 45 30 30 50 60 45 45 45 45(mm) of second curved portion Length L2 of first curved — 60 60 60 60 6030 40 50 70 portion/length L1 of curved groove (%) Steering stability on100 100 99 100 100 101 99 100 100 99 dry road surface (score) On-snowperformance 100 105 106 105 104 103 103 104 105 104 (score)

As a result of the tests, it was confirmed that the tire of each Exampleexhibits excellent on-snow performance while maintaining steeringstability on a dry road surface in a preferable range, and the overallperformance of the tire is improved.

What is claimed is:
 1. A tire having a tread portion, wherein the treadportion includes a first land portion, the first land portion includes afirst circumferential edge, a second circumferential edge, and a treadsurface between the first circumferential edge and the secondcircumferential edge, on the first land portion, a plurality of curvedgrooves are provided in a tire circumferential direction, each of thecurved grooves extends from a first end on the first circumferentialedge side and terminates at a second end within the first land portion,each of the curved grooves includes a first curved portion on the firstend side, and a second curved portion on the second end side, the firstcurved portion is an arc curve with a radius of curvature having acenter on the first circumferential edge side of the curved groove, thesecond curved portion is an arc curve with a radius of curvature havinga center on the second circumferential edge side of the curved groove,and the radius of curvature of the first curved portion is 10 to 30 mm.2. The tire according to claim 1, wherein the radius of curvature of thesecond curved portion is 30 to 60 mm.
 3. A tire having a tread portion,wherein the tread portion includes a first land portion, the first landportion includes a first circumferential edge, a second circumferentialedge, and a tread surface between the first circumferential edge and thesecond circumferential edge, on the first land portion, a plurality ofcurved grooves are provided in a tire circumferential direction, each ofthe curved grooves extends from a first end on the first circumferentialedge side and terminates at a second end within the first land portion,each of the curved grooves includes a first curved portion on the firstend side, and a second curved portion on the second end side, the firstcurved portion is an arc curve with a radius of curvature having acenter on the first circumferential edge side of the curved groove, thesecond curved portion is an arc curve with a radius of curvature havinga center on the second circumferential edge side of the curved groove,and the first land portion comprises an inclined groove that is inclinedfrom the second circumferential edge and crosses the first curvedportion of the curved groove.
 4. The tire according to claim 3, whereinthe first curved portion crosses a center position in a tire axialdirection of the first land portion, the second curved portion crosses acenter position in a tire axial direction of the first land portion, thesecond end is located between the first circumferential edge and acenter position in a tire axial direction of the first land portion, andthe radius of curvature of the second curved portion is larger than theradius of curvature of the first curved portion.
 5. A tire having atread portion, wherein the tread portion includes a first land portion,the first land portion includes a first circumferential edge, a secondcircumferential edge, and a tread surface between the firstcircumferential edge and the second circumferential edge, on the firstland portion, a plurality of curved grooves are provided in a tirecircumferential direction, each of the curved grooves extends from afirst end on the first circumferential edge side and terminates at asecond end within the first land portion, each of the curved groovesincludes a first curved portion on the first end side, and a secondcurved portion on the second end side, the first curved portion is anarc curve with a radius of curvature having a center on the firstcircumferential edge side of the curved groove, the second curvedportion is an arc curve with a radius of curvature having a center onthe second circumferential edge side of the curved groove, the tire hasa designated mounting direction to a vehicle, the tread portion includesa first tread edge located on an outer side of the vehicle when the tireis mounted on the vehicle, a second tread edge located on an inner sideof the vehicle when the tire is mounted on the vehicle, a first shouldermain groove continuously extending in the tire circumferential directionbetween the first tread edge and a tire equator, and a crown main grooveadjacent to the second tread edge side of the first shoulder maingroove, and the first land portion is demarcated between the firstshoulder main groove and the crown main groove, and further comprising afirst sipe that extends from the first circumferential edge to a secondinclined groove parallel to the first curved portion of the curvedgroove.
 6. The tire according to claim 5, wherein the first curvedportion crosses a center position in a tire axial direction of the firstland portion.
 7. The tire according to claim 5, wherein the secondcurved portion crosses a center position in a tire axial direction ofthe first land portion.
 8. The tire according to claim 5, wherein thesecond end is located between the first circumferential edge and acenter position in a tire axial direction of the first land portion. 9.The tire according to claim 5, wherein a groove width of each of thecurved grooves gradually decreases from the first end toward the secondend.
 10. The tire according to claim 5, wherein a groove width of eachof the curved grooves is 2 to 4 mm.
 11. The tire according to claim 5,wherein the radius of curvature of the second curved portion is largerthan the radius of curvature of the first curved portion.
 12. The tireaccording to claim 5, wherein the radius of curvature of the firstcurved portion is 10 to 30 mm.
 13. The tire according to claim 5,wherein the radius of curvature of the second curved portion is 30 to 60mm.
 14. The tire according to claim 5, wherein a length in the tirecircumferential direction of the first curved portion is 30% to 70% of alength in the tire circumferential direction of the curved groove. 15.The tire according to claim 5, wherein the tread portion includes fourland portions demarcated by main grooves continuous in the tirecircumferential direction.
 16. The tire according to claim 5, whereinthe first land portion comprises an inclined groove that is inclinedfrom the second circumferential edge and crosses the first curvedportion of the curved groove.
 17. The tire according to claim 5, furthercomprising a lateral groove that overlaps a region obtained by extendingan end portion on a first shoulder main groove side of the curvedgroove.
 18. The tire according to claim 5, wherein the first curvedportion comprises a first portion and a second portion, the secondportion provided with a tie bar raised at a groove bottom in a centerportion in the longitudinal direction of the second portion.
 19. Thetire according to claim 5, further comprising a second sipe that extendsfrom the first circumferential edge to the second curved portion of thecurved groove.